Room Light Control Sujatha

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Automatic Room Light Control

Abstract:

Automatic Room Light Control System is a simple yet powerful concept, which uses

transistor as a switch. By using this system manual works are 100% remoe!. "t

automatically switches #$ lights when the sunlight goes elow the isile region of our eyes.

&his is !one y a sensor calle! Light 'epen!ant Resistor (L'R) which senses the light

actually like our eyes. "t automatically switches #** lights wheneer the sunlight comes,

isile to our eyes.

By using this system energy consumption is also re!uce! ecause nowa!ays the manually

operate! room lights are not switche! off een the sunlight comes an! also switche! on

earlier efore sunset. "n this pro+ect, no nee! of manual operation like #$ time an! #** time

setting.

&his pro+ect clearly !emonstrates the working of transistor in saturation region an! cutoff

region. &he working of relay is also known.

# 504,5thFloor, Manzil Chamber, Mehdipatnam, Hyd. -28, A.P. !"A. eb$ite%&&&.int$.in 'el. !o$. % ()* ))85*+848, ()*

)05*2*50*58 -mail% onnet2int$/mail.om
mailto:[email protected]:[email protected]


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BL#C- '"ARA/

LDR:

L'Rs or Light 'epen!ent Resistors are ery useful especially in light!ark sensor circuits.

$ormally the resistance of an L'R is ery high, sometimes as high as 1000 000 ohms, ut

when they are illuminate! with light resistance !rops !ramatically.



1*

Po&er

1elay

!3

Common

!C

1$

"1

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2hen the light leel is low the resistance of the L'R is high. &his preents current from

flowing to the ase of the transistors. Conse3uently the L4' !oes not light.

5oweer, when light shines onto the L'R its resistance falls an! current flows into the ase

of the first transistor an! then the secon! transistor. &he L4' lights.

5ere in our pro+ect to aoi! the light from le! to fall on to L'R we place a o6 in which we

will keep our +ewelry. "f any one remoes the o6 the light from le! falls !irectly on to the

L'R an! then the transistor will e on which is monitore! y the microcontroller.

Light-emitting diode (LED)

Lightemitting !io!es are elements for light signali7ation in electronics. &hey are

manufacture! in !ifferent shapes, colors an! si7es. *or their low price, low consumption an!

simple use, they hae almost completely pushe! asi!e other light sources uls at first place.

&hey perform similar to common !io!es with the !ifference that they emit light when current

flows through them.




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"t is important to know that each !io!e will e imme!iately !estroye! unless its current is

limite!. &his means that a con!uctor must e connecte! in parallel to a !io!e. "n or!er to

correctly !etermine alue of this

con!uctor, it is necessary to know!io!e8s oltage !rop in forwar!

!irection, which !epen!s on what

material a !io!e is ma!e of an! what

colour it is. 9alues typical for the most

fre3uently use! !io!es are shown in

tale elow As seen, there are three

main types of L4's. Standardones get

ful rightness at current of :0mA.Low Current!io!es get ful rightness at ten times lower

current while Super Bright!io!es pro!uce more intensie light than Stan!ar! ones.

Since the ;0


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"n!uctor

Fig: Circuit symbol o a relay

!"eration:

2hen current flows through the coil, a magnetic fiel! is create! aroun! the coil i.e.,

the coil is energi7e!. &his causes the armature to e attracte! to the coil. &he armature8s

contact acts like a switch an! closes or opens the circuit. 2hen the coil is not energi7e!, a

spring pulls the armature to its normal state of open or close!. &here are all types of relays for

all kin!s of applications.




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Fig: Relay !"eration and use o "rotection diodes

&ransistors an! "Cs must e protecte! from the rief high oltage =spike= pro!uce! when

the relay coil is switche! off. &he aoe !iagram shows how a signal !io!e (eg 1$>1>;) is

connecte! across the relay coil to proi!e this protection. &he !io!e is connecte! =ackwar!s=

so that it will normally not con!uct. Con!uction occurs only when the relay coil is switche!

off, at this moment the current tries to flow continuously through the coil an! it is safely

!ierte! through the !io!e. 2ithout the !io!e no current coul! flow an! the coil woul!

pro!uce a !amaging high oltage =spike= in its attempt to keep the current flowing.

"n choosing a relay, the following characteristics nee! to e consi!ere!

1. &he contacts can e normally open ($#) or normally close! ($C). "n the $C type, the

contacts are close! when the coil is not energi7e!. "n the $# type, the contacts are close!

when the coil is energi7e!.

:. &here can e one or more contacts. i.e., !ifferent types like S?S& (single pole single

throw), S?'& (single pole !oule throw) an! '?'& (!oule pole !oule throw) relays.

@. &he oltage an! current re3uire! to energi7e the coil. &he oltage can ary from a few

olts to


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>. &he minimum 'CAC oltage an! current that can e han!le! y the contacts. &his is in

the range of a few olts to hun!re!s of olts, while the current can e from a few amps to

>0A or more, !epen!ing on the relay.

DR#$#%& A RELAY:

An S?'& relay consists of fie pins, two for the magnetic coil, one as the common

terminal an! the last pins as normally connecte! pin an! normally close! pin. 2hen the

current flows through this coil, the coil gets energi7e!. "nitially when the coil is not

energi7e!, there will e a connection etween the common terminal an! normally close! pin.

But when the coil is energi7e!, this connection reaks an! a new connection etween the

common terminal an! normally open pin will e estalishe!. &hus when there is an input

from the microcontroller to the relay, the relay will e switche! on. &hus when the relay is

on, it can !rie the loa!s connecte! etween the common terminal an! normally open pin.

&herefore, the relay takes


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'!ER S''LY:

&he input to the circuit is applie! from the regulate! power supply. &he a.c. input i.e., :@09

from the mains supply is step !own y the transformer to 1:9 an! is fe! to a rectifier. &he

output otaine! from the rectifier is a pulsating !.c oltage. So in or!er to get a pure !.c

oltage, the output oltage from the rectifier is fe! to a filter to remoe any a.c components

present een after rectification. $ow, this oltage is gien to a oltage regulator to otain a

pure constant !c oltage.

Fig: 'o*er su""ly

+ransormer:

sually, 'C oltages are re3uire! to operate arious electronic e3uipment an! these

oltages are


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&he output from the transformer is fe! to the rectifier. "t conerts A.C. into pulsating

'.C. &he rectifier may e a half wae or a full wae rectifier. "n this pro+ect, a ri!ge rectifier

is use! ecause of its merits like goo! staility an! full wae rectification.

Filter:

Capacitie filter is use! in this pro+ect. "t remoes the ripples from the output of

rectifier an! smoothens the '.C. #utput receie! from this filter is constant until the mains

oltage an! loa! is maintaine! constant. 5oweer, if either of the two is arie!, '.C. oltage

receie! at this point changes. &herefore a regulator is applie! at the output stage.

$oltage regulator:

As the name itself implies, it regulates the input applie! to it. A oltage regulator is anelectrical regulator !esigne! to automatically maintain a constant oltage leel. "n this

pro+ect, power supply of


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Room Light Control Sujatha